D20509: Detect duplicate ANDROID_EXTRA_LIBS and minor bug fix

[Luca Beltrame]

lbeltrame added reviewers: apol, vkrause.

REPOSITORY
  R240 Extra CMake Modules

REVISION DETAIL
  https://phabricator.kde.org/D20509

To: sh-zam, apol, vkrause
Cc: kde-buildsystem, kde-frameworks-devel, bencreasy, michaelh, ngraham, bruns